Digestion

Deglutition(Swallowing):

The food is tasted in the oral cavity and mixed with saliva.The bolus (mass of food) is pushed inward through the pharynx into the oesophagus.This process is called swallowing or deglutition.It involves three stages : (i)The Voluntary Stage. The bolus is forced to move from the oral cavity into the pharynx(oropharynx).(ii)The Pharyngeal Stage.This is involuntary stage.The bolus is passed from the pharynx into the oesophagus.(iii)The Oesophageal Stage.This also represents the involuntary stage.The bolus passes through the laryngopharynx and enters the oesophagus in 1 to 2 seconds.Swallow is controlled by a swallowing center located in the Medulla Oblongata and lower Pons Varolli of the brain.

Peristalsis:

It is a reflex wave of relaxation in front of the content following a wave of contraction traveling down the tubular viscera by which contents are pushed through.It occurs in tubular viscera(i.e. oesophagus,stomach,intestine, etc.). Peristalsis is controlled by Medulla Oblongata.

Action of Digestive Enzymes in Human :

Saliva or Salivary Juice(Salivary Gland):

Salivary Amylase(Ptyalin) converts starch(polysaccharide) into Disaccharides in mouth.

Gastric Juice(Stomach):

i)Pepsin converts proteins into large peptides.

ii)Renin converts casein(milk protein) into calcium paracaseinate in the child’s stomach.

iii)Gastric Lipase converts small amount of fat into Glycerol and fatty acids.

Pancreatic Juice(Pancreas) –Site of action is Small Intestine.

i)Pancreatic α-amylase converts starch into Disaccharides

ii)Trypsin converts proteins into large peptides.

iii)Chymotrypsin converts proteins into large peptides.

iv)Elastase converts elastin(protein) into large peptides.

v)Carboxypeptidases converts large peptides into dipeptides and amino acid.

vi)Pancreatic lipase converts fats(Triglycerides) into fatty acids and glycerol.

vii)Nuclease:(a)Deoxyribonuclease converts DNA into deoxyribonucleotides.(b)Ribonuclease converts RNA into Ribonucleotides.

Intestinal Juice(Small Intestine)- Site of action is small intestine.

i)Enterokinase converts Trypsinogen into Trypsin.

ii)Aminopeptidases converts Large peptides into Dipeptides and amino acid.

iii)Dipeptidases converts Dipeptides into Amino Acids.

iv)Disaccharidases converts Disaccharides into Monosaccharides.

v)Intestinal Lipase converts Fats(Glycerides) into Fatty acids and Glycerol.

vi)Nucleotidases converts Nucleotides into Nucleosides and Inorganic Phosphate.

vii)Nucleosidases converts Nucleosides into Nitrogenous bases and Pentose sugar.

Action of Gastrointestinal Hormones:

i)When food enters the stomach then distention of stomach occurs resulting the production of Gastrin hormone by Pyloric stomach and Duodenum.Gastrin stimulates gastric gland to secrete and release the Gastric Juice.It also stimulates gastric mobility.

ii)When chyme enters into the Duodenum then Enterogasterone(Gastric Inhibitory Peptide-GIP) hormone is released by Duodenum that inhibits the gastric secretion and mobility(slow gastric contraction) of stomach.

iii)Secretin(1^st hormone discovered by scientist) is secreted by Duodenum and Jejunum when acidic chyme enter into the Duodenum.This hormone release bicarbonate in the pancreatic juice,increase secretion of bile,decreases gastric secretion.

iv)Cholecystokinin-pancreozymin(CCK-Pz) secreted by small intestine and is stimulus to presence of fats in the Duodenum.It stimulates the contraction of Gall Bladder to release bile,stimulates Pancreas to secrete and release digestive enzymes in the pancreatic juice.

v)Duocrinin is secreted by Duodenum and is stimulus to presence of acidic chyme in intestine.It stimulates the Brunner’s glands to release mucus and enzymes into the intestinal juice.

vi)Enterocrinin secreted by small intestine and is stimulus to presence of acidic chyme in small intestine.It stimulates the Cryps of Lieberkuhn to release enzymes into the intestinal juice.

vii)Vasoactive Intestinal Peptide(VIP) is secreted by small intestine and is stimulus to presence of food in the small intestine.It stimulates stomach and small intestine to dilate peripheral blood vessels of gut and inhibits gastric acid secretion.

viii)Villikinin is secreted by small intestine and is stimulus to presence of food in small intestine.It accelerates the villi movement of small intestine.